Plastic has low thermal conductivity than inorganic substances such as metal materials. Therefore, there has conventionally been a problem that generated heat is not easily dissipated when thermoplastic resin molded articles are used for various items such as casings of personal computers or displays, materials of electronic devices, automotive interiors or exteriors, illumination members, and portable electronic devices like mobile phones. In order to solve this problem, it has been widely attempted to obtain a highly thermally conductive resin composition by mixing, with a thermoplastic resin, a large amount of a highly thermally conductive inorganic substance. Examples of such a highly thermally conductive inorganic compound encompass highly thermally conductive inorganic fillers such as graphite, carbon fiber, low-melting metal, alumina, and aluminum nitride. A thermoplastic resin composition filled with a large amount of such a filler has a problem that, since being filled with the large amount of the filler, the thermoplastic resin composition has extremely low weld strength.
As a method of increasing weld strength of a thermoplastic resin, Patent Literature 1 discloses, for example, a method in which an organic compound whose functional group is controlled is used for a thermoplastic resin composition filled with a small amount of a filler. However, according to the method disclosed in Patent Literature 1, it is necessary to produce the organic compound. Therefore, there are problems of costs and of time and effort. Meanwhile, Patent Literature 2 discloses, as an example, a method in which glass fiber having a given aspect ratio is used for a thermoplastic resin composition filled with a small amount of a filler. According to the method, a step of controlling a length of the glass fiber is needed after the glass fiber is melt-kneaded together with the thermoplastic resin composition. Moreover, the filler with which the thermoplastic resin composition is filled is limited to particular one and therefore, the thermoplastic resin composition may not be filled with a large amount of another filler. In a case where a thermoplastic resin is filled with a large amount of a filler, problems newly arise such that the thermoplastic resin has low moldability and has a weld portion low in strength.
In regard to a thermoplastic resin filed with a large amount of a filler, it has been thus difficult to produce, with use of the thermoplastic resin, a composition having excellent weld strength.